1. Field of the Invention
The present invention relates to a method for reducing an amount of marking material to be used for printing an image on a receiving material using a print process. The present invention further relates to a print engine, configured to perform said method.
2. Description of the Related Art
Many known print processes for reproducing documents and images are arranged to work with a binary print signal that indicates whether or not a fixed amount of marking material is to be applied for a predefined print pixel. The marking material is for example toner or ink. The print pixels are regularly distributed on a receiving material. In color print processes, several process colors are used to obtain a full color output, each of the process colors being developed individually by an associated binary print signal.
A binary image is usually a two-dimensional array of pixels, wherein each image pixel has one of two values that indicates whether or not to mark a print pixel associated with the image pixel. In a print engine, binary images are used to generate the print signals for the various process colors. The binary images may stem from a computing device that accepts print jobs and transforms images from documents to be printed into printable data by applying different methods of image processing, among which color management, smoothing and sharpening, brightness and contrast adjustment, and halftoning. A binary image for a print engine is printer specific, meaning that the printed output of one and the same binary image on different print engines may be different.
It is advantageous to be able to influence the quality of the printed output by selecting various settings for the image processing modules, such as the amount of sharpening to be applied, the amount of contrast, etc., along with settings that may be selected for the print job, such as whether or not a staple is needed, if the job is to be printed one- or double-sided, etc. It is possible, for example, to make the printed output look lighter, thereby using less toner, by selecting a setting affecting the lightness in one of the image processing modules, such as a transfer function or a halftoning module. However, once a binary image is transmitted to the print engine, it is usually not possible anymore to change the appearance or characteristics of the image.
In some print processes, it is necessary to reduce the amount of marking material, since the receiving material is unable to handle the maximum amount that may be applied locally. This may be done in the image processing modules, but, since the amount of reduction may depend on the receiving material that is used, it is advantageous to be able to do this reduction after the binary image is transmitted to the print engine. Various names are used for such reduction method, among which dot thinning, toner save method, ink reduction etc. The reduction of marking material may also be wanted for economical reasons to reduce the cost of the printed output, or for ecological reasons.
In U.S. Pat. No. 5,237,344, a method for dot thinning is described for ink jet processes in which a local dot density is calculated and thinning means are activated to reduce the number of dots that are discharged on the recording medium. The thinning information is pre-stored in a memory with the font data. In U.S. Pat. No. 5,563,985, the dot thinning is extended to color printing. The thinning means herein use a random selection of pixels that are set to OFF to prevent moire between the thinning patterns of the various process colors. In U.S. Pat. No. 5,483,625, a regular thinning pattern is used in combination with horizontal and vertical line preservation to prevent features to be washed out of an image and text becoming unrecognizable. All these methods use a kind of selection mechanism to determine if a print position may be elected for withholding its marking material that otherwise would be transferred to the receiving medium. This selection mechanism leads to rather complicated electronic circuits.
An object of the invention is to provide a simple method for reducing the amount of toner in the printed output from a binary image without affecting the information content of the image.